This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Several ion channels are being studied with the plan of determining the molecular mechanism of their action. These include voltage gated channels responsible for propagation and termination of action potentials, calcium channels involved in signal amplification and ligand gated ion channels involved in signal detection and modulation. Using rapid affinity purification methods, along with x-ray crystallography and electron microscopy, our goal is to elucidate the structural elements of these channels in various state. Systems of current interest include the prokaryotic mechanosensitive channels (Msc), including those of large (MscL) and small (MscS) conductance that couple channel gating with membrane tension. We have begun to collect cryo-tomograms of membrane preparations of prokaryotes that contain mechanosensitive channels and are applying 3D volume averaging using out PEET software program.